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        <p>Library Version 11.2.5.3</p>
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            <h2 class="title"><a id="persist_index"></a>Chapter 4. Working with Indices</h2>
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      <div class="toc">
        <p>
          <b>Table of Contents</b>
        </p>
        <dl>
          <dt>
            <span class="sect1">
              <a href="persist_index.html#dplindexaccess">Accessing Indexes</a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="sect2">
                  <a href="persist_index.html#primaryindexaccess">Accessing Primary Indices</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="persist_index.html#secondaryindexaccess">Accessing Secondary Indices</a>
                </span>
              </dt>
            </dl>
          </dd>
          <dt>
            <span class="sect1">
              <a href="dplindexcreate.html">Creating Indexes</a>
            </span>
          </dt>
          <dd>
            <dl>
              <dt>
                <span class="sect2">
                  <a href="dplindexcreate.html#dplprimaryidxdecl">Declaring a Primary Indexes</a>
                </span>
              </dt>
              <dt>
                <span class="sect2">
                  <a href="dplindexcreate.html#dplsecondaryidxdecl">Declaring Secondary Indexes</a>
                </span>
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              <dt>
                <span class="sect2">
                  <a href="dplindexcreate.html#foreignkey">Foreign Key Constraints</a>
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      <p>
          All entity classes stored in DB using the DPL must have a
          primary index, or key, identified for them. All such classes may
          also have one or more secondary keys declared for them. This
          chapter describes primary and secondary indexes in detail, and
          shows how to access the indexes created for a given entity class.
  </p>
      <p>
            One way to organize access to your primary and secondary
            indexes is to create a <span class="emphasis"><em>data accessor</em></span>
            class. We show an implementation of a data accessor class in 
            <a class="xref" href="simpleda.html" title="SimpleDA.class">SimpleDA.class</a>.
    </p>
      <div class="sect1" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h2 class="title" style="clear: both"><a id="dplindexaccess"></a>Accessing Indexes</h2>
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        <div class="toc">
          <dl>
            <dt>
              <span class="sect2">
                <a href="persist_index.html#primaryindexaccess">Accessing Primary Indices</a>
              </span>
            </dt>
            <dt>
              <span class="sect2">
                <a href="persist_index.html#secondaryindexaccess">Accessing Secondary Indices</a>
              </span>
            </dt>
          </dl>
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        <p>
                  In order to retrieve any object from an entity store, you
                  must access at least the primary index for that object.
                  Different entity classes stored in an entity store can have
                  different primary indexes, but all entity classes must have a
                  primary index declared for it. The primary index is just
                  the default index used for the class. (That is, it is the
                  data's primary <span class="emphasis"><em>key</em></span> for the underlying database.)
          </p>
        <p>
                  Entity classes can optionally have secondary indexes
                  declared for them. In order to access these secondary
                  indexes, you must first access the primary index. 
          </p>
        <div class="sect2" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="primaryindexaccess"></a>Accessing Primary Indices</h3>
              </div>
            </div>
          </div>
          <p>
                            You retrieve a primary index using the
                            <code class="methodname">EntityStore.getPrimaryIndex()</code>
                            method. To do this, you indicate the index key type
                            (that is, whether it is a String, Integer, and
                            so forth) and the class of the entities stored
                            in the index.
                    </p>
          <p>
                        For example, the following retrieves the
                        primary index for an <code class="classname">Inventory</code>
                        class (we provide an implementation of this class in
                        <a class="xref" href="inventoryclass.html" title="Inventory.java">Inventory.java</a>). 
                        These index keys are of type <code class="classname">String</code>.
                    </p>
          <pre class="programlisting">PrimaryIndex&lt;String,Inventory&gt; inventoryBySku = 
    store.getPrimaryIndex(String.class, Inventory.class); </pre>
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        <div class="sect2" lang="en" xml:lang="en">
          <div class="titlepage">
            <div>
              <div>
                <h3 class="title"><a id="secondaryindexaccess"></a>Accessing Secondary Indices</h3>
              </div>
            </div>
          </div>
          <p>
                            You retrieve a secondary index using the
                            <code class="methodname">EntityStore.getSecondaryIndex()</code>
                            method. Because secondary indices actually
                            refer to a primary index somewhere in your data
                            store, to access a secondary index you:
                    </p>
          <div class="orderedlist">
            <ol type="1">
              <li>
                <p>
                                            Provide the primary index as
                                            returned by
                                            <code class="methodname">EntityStore.getPrimaryIndex()</code>.
                                    </p>
              </li>
              <li>
                <p>
                                            Identify the key data type used by
                                            the secondary index
                                            (<code class="classname">String</code>,
                                            <code class="classname">Long</code>,
                                            and so forth).
                                    </p>
              </li>
              <li>
                <p>
                                            Identify the name of the
                                            secondary key field.
                                            When you declare the
                                            <code class="classname">SecondaryIndex</code>
                                            object, you identify the entity class
                                            to which the secondary index
                                            must refer.
                                    </p>
              </li>
            </ol>
          </div>
          <p>
                        For example, the following first retrieves the
                        primary index, and then uses that to retrieve a secondary
                        index. The secondary key is held by the
                        <code class="literal">itemName</code> field of the
                        <code class="classname">Inventory</code> class.
                    </p>
          <pre class="programlisting">PrimaryIndex&lt;String,Inventory&gt; inventoryBySku = 
store.getPrimaryIndex(String.class, Inventory.class); 

SecondaryIndex&lt;String,String,Inventory&gt; inventoryByName = 
    store.getSecondaryIndex(inventoryBySku, String.class, "itemName"); </pre>
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